Thanks everyone for your ideas.
This topic is so big that It's really hard to make it work.

I was thinking maybe I have master nodes and i also have POW. so imagine I use pow and pos together, which means, that blockchain will be alike (block1, block2, Master-node block, block3,block4, master-node block) . so no one will be able to add 3 blocks simultaneously if he mines privately. does that make sense? I don't know , can you give me at least example if preventing this problem made some coin makers use pow and pos together?